Is that leafhopper or boron deficiency in my alfalfa?

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Is that leafhopper or boron deficiency
in my alfalfa?

Author:	Keith Reid - Soil Fertility Specialist/OMAFRA
Creation Date:	04 August 2005
Last Reviewed:	04 August 2005

Alfalfa regrowth, particularly during dry weather conditions, often suffers from stunting and yellowing in the field. The most common causes of this are feeding injury from potato leafhoppers, or a deficiency of boron in the plant. Diagnosing which is the problem is critical to deciding what corrective action to take.

	Potato Leafhopper Injury	Boron Deficiency
Leaf Symptoms	"V" shaped injury at tip of leaflet, with yellowing of leaf area around the injury	Discolouration of leaflets, ranging in hue from yellow to red or purple.
Plant Symptoms	Stunting of the plant beyond injured leaflets, as toxin in leafhopper saliva stops further growth	Shortened internodes, so entire plant is stunted. Upper leaves may form a whorl as stem fails to elongate.
Pattern in Field	General across the field, or sometimes concentrated in the lee of fencerows where the slow wind allows the leafhoppers to land. Not affected by soil type.	Concentrated in driest parts of the field, particularly on eroded knolls in excessively drained soils. More common in central Ontario than the rest of the province.
Antecedent Weather	Hot, dry conditions that allow populations of leafhoppers to build up.	Dry weather increases the incidence of boron deficiency, irrespective of temperature.
Diagnostic Tests	Sweep net to collect leafhoppers from field. Threshold for treatment increases as alfalfa gets bigger:	Tissue tests or visual plant symptoms can be effective. Soil tests cannot reliably detect deficiencies.
Corrective Action	A number of insecticides can provide excellent control. Check the label for pre-harvest intervals. Insect numbers will be greatly reduced by a heavy rainfall, as they are washed off the plants, and as conditions favour the fungus diseases that give natural control.	On fields with a history of boron deficiency, include 1-2 kg/ha of boron in the regular fertilizer applications to the field. B will be most effective if applied following the first cut, rather than in the fall or early spring.

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